Relationship between Solitary Masturbation and Sexual Satisfaction: A Systematic Review

Masturbation is a healthy sexual behavior associated with different sexual functioning dimensions, which highlights sexual satisfaction as an important manifestation of sexual wellbeing. This review aims to systematically examine studies that have associated masturbation with sexual satisfaction, both in individuals with and without a partner. Following the PRISMA statement, searches were made in the APA PsycInfo, Medline, Scopus, and Web of Science databases. The search yielded 851 records, and twenty-two articles that examined the relation between solitary masturbation and sexual satisfaction were selected. In men, a negative relation between masturbation and sexual satisfaction was observed in 71.4% of the studies, 21.4% found no such relation, and 7.2% observed a positive association. In women, 40% reported no relation, 33.3% a negative relation, and 26.7% a positive one. The negative association between solitary masturbation and sexual satisfaction is consistent with the previously proposed compensatory role of masturbation, especially for men. In women, compared to men, the complementary role of masturbation in relation to sexual relationships is observed to a greater extent and is associated more closely with sexual health. The importance of including different parameters beyond the masturbation frequency in future studies to explore its relation with sexual satisfaction is emphasized. This systematic review is registered in PROSPERO (CRD42023416688).


Introduction
Masturbation is a healthy sexual behavior practiced with others (e.g., a partner) or individually [1].Solitary masturbation is defined as erotic self-stimulation without anyone else being present or participating [2].Its practice is present from very early development phases to old age [3].This behavior favors self-exploration and sexual learning in a context in which the presence of sexual difficulties might be less prevalent [4].Previous studies have stressed the importance of solitary masturbation for the adjustment and generalization of the sexual response to the context of sexual relationships [5], acting as a therapeutic tool to deal with some sexual difficulties [6,7].
The relation of solitary masturbation with sexual relationships has been studied mostly by two models: compensatory and complementary.The compensatory model hypothesizes that masturbation frequency could increase for the purpose of substituting unsatisfactory or insufficient sexual relationships [8,9].The complementary model considers a positive relation between masturbation behavior and sexual relationships, implying that practicing one would be associated with the other one being practiced more frequently [9].Previous pieces of evidence suggest that the compensatory pattern would be more present in men, with the complementary pattern in women [9][10][11][12][13][14], despite some studies showing the independence of gender in both of these models [15,16].
Masturbation has been related to different sexual functioning dimensions, although very few results have been obtained.Positive associations have been described with sexual desire [17], sexual arousal [11], or orgasm [5], which evidences the positive implication of this behavior in sexual response.One of the most interesting dimensions is sexual satisfaction, which is an important indicator of sexual health [18][19][20].
Sexual satisfaction could be considered the last phase of the sexual response cycle according to Basson's model [21,22] and is defined as "an affective response arising from one's subjective evaluation of the positive and negative dimensions associated with one's sexual relationship" [23] (p.268).Its study requires a multidimensional approach that contemplates personal, interpersonal, and social factors [19,24].In line with this, the Ecological Theory of Human Development [25] has served as a guide to study it by bearing in mind the different associated relevant variables, which range from the closest to the most distant to an individual [19].Of the variables associated with sexual satisfaction, solitary masturbation falls under personal-type factors [13,26,27].
As far as we are aware, the pieces of evidence that have associated solitary masturbation with sexual satisfaction have not been integrated, despite its importance for sexual health.Thus, considering that previous literature reviews on this are missing, the objective of the present study is to systematically analyze the results obtained in the scientific literature about the relation between solitary masturbation (i.e., its presence/absence and/or frequency) and sexual satisfaction, including a comparison of this relation in men and women.

Materials and Methods
This systematic review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Guidelines (PRISMA) [28].The protocol of this review is registered in PROSPERO (registration number: CRD42023416688).

Eligibility Criteria
To fulfill the objectives of this systematic review, the considered studies had to address the relation between solitary masturbation and sexual satisfaction.Eligible studies had to meet all the following inclusion criteria: (a) original research articles; (b) solitary masturbation (as presence/absence or frequency); (c) sexual satisfaction was assessed using standardized instruments, ad hoc items, or derived from scales, questionnaires, or interviews; (d) they had examined the direct and indirect relation, considering mediators and/or covariates between solitary masturbation and sexual satisfaction.
There was no limitation for publication year, and the English and Spanish languages were considered.

Information Sources
The literature search was conducted on APA PsycInfo, Medline, Scopus, and Web of Science.The last database query date was 30 October 2023.

Search Strategy
Following the recommendations by Quevedo-Blasco [29] and using the terms related to sexual satisfaction as employed in the systematic review by Sánchez-Fuentes et al. [19], the search strategy integrated the following terms: (masturb* OR self-stimulat* OR onanism* OR "solitary sexual activit*") AND ("satisfac* sex*" OR "sex* satisfact*" OR "satisfaction with sex*"), using the truncation "*" to include any variant of words.
To validate the search strategy, a peer review was conducted by proofreading the syntax, spelling, and structure and ensuring that the search formula identified articles that were relevant to the search.The formula was applied to the title, abstract, and/or keywords, or, if applicable, to the topic, to narrow down the search on the topic of masturbation and sexual satisfaction.

Selection Process
The search results were exported on the Rayyan online platform, a web-based automated screening tool developed by the Qatar Computing Research Institute (QCRI) that is accessible at www.rayyan.ai(accessed on 15 November 2023) [30].This export included the title, authors, publication date, abstract, and keywords.Two authors (AÁM and OC) independently reviewed the documents based on their title, abstract, and keywords by categorizing articles as included, doubtful, or rejected.The studies labeled as doubtful underwent a full-text review, and discrepancies were solved by consensus.Final decisions, if necessary, were made by a third researcher (JCS).

Data Collection Process
The articles that met the inclusion criteria were comprehensively read independently by two reviewers to guarantee the objectivity and rigor of the results.A data collection form was designed, and the extracted data were compared to any discrepancies resolved by discussion.The extracted data included: (a) authors, (b) country, (c) sample, (d) participants' sexual orientation, (e) instrument used to assess solitary masturbation, (f) instrument applied to assess sexual satisfaction, and (g) results about the association between masturbation and sexual satisfaction.The true Kappa value was employed to assess the reliability of coding [31,32].Intercoding was evaluated by indicating agreement or disagreement in the analyses of the categories extracted during the article selection process [33].A true Kappa value of 0.91 was obtained when considering the agreement between coders to be satisfactory with a Kappa value above 75%.

Data Items
Outcome measures that assess (a) solitary masturbation and (b) sexual satisfaction were extracted.The results can be reported as the presence/absence of solitary masturbation by dichotomous items, a frequency scale of solitary masturbation, or interviews.Likewise, an overall test score to provide a general measure of sexual satisfaction (e.g., general sexual satisfaction) or subscales/specific items to provide a measure of domain-specific sexual satisfaction (i.e., physical sexual satisfaction) was/were considered.

Study Risk of Bias Assessment
The risk of bias in the included studies was assessed using the Quality Assessment Tool for Observational Cohort and Cross-Sectional Studies (QATOCCS) [34] for those studies that indicated a quantitative methodology and the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) [35] tool for the studies that indicated an observational analytical methodology.These tools provided a standardized framework for assessing the scientific rigor of all the reviewed studies through a checklist of requirements (e.g., definition of the study population, the research question, control definition, inclusion criteria, blindness, and the reporting of confounders).The evaluation ensured the studies' robustness and the results' reliability.To do so, two authors independently applied the tools to the included studies.If discrepancies arose, they were solved by consensus.

Synthesis Methods
Table 1 shows the individual results of the studies and the synthesis.For better visualization purposes, the authors, publication year, country, sample size, assessment of masturbation and sexual satisfaction, and the main findings about the relation between both variables were tabulated.Not specified.
Ad hoc item to ask about the number of times the participant has masturbated in the last month.
Four single-item ad hoc questions rated on a Likert scale of 1 (strongly disagree) to 7 (strongly agree) to assess four dimensions of sexual satisfaction: (a) "I have been satisfied with quality of genital stimulation and/or intercourse I've had with a partner" (stimulation/intercourse), (b) "I have been satisfied with the quality of sexual/erotic contact I've had with a partner that did not include or lead to sustained genital stimulation or intercourse" (sexual/erotic contact), (c) "I have been satisfied with my sex life in the last three months" (3 months), and (d)"On the whole, I have been satisfied with my sexual life" (overall satisfaction).
The frequency of masturbation is not associated with satisfaction with sexual/erotic contact, satisfaction in the last three months, or overall satisfaction (lifetime sexual satisfaction).Masturbation in the last 30 days is negatively related to satisfaction with stimulation/intercourse or genital stimulation.Covariates in regression models include family affection, partner initiation, and communication.

Brody and
Costa [37] Sweden 2810 (1255 men and 1129 women) with or without a partner, from 18 to 74 years old (M men = 40.9;M women = 40.8).
Not specified.
Ad hoc item para frequency of masturbation in the past 30 days.
Satisfaction scale comes from different versions of the Life Satisfaction Scale: LiSat-8 [38] and LiSat-11 [39].They assess their satisfaction with their sex life on a six-point Likert-type scale, anchored with 1 = very unsatisfying and 6 = very satisfying.
The frequency of masturbation was inversely related to nearly all indices of sexual satisfaction in both men and women, with a small to medium effect size.Covariates: age, penile-vaginal intercourse, anal sex, and oral sex.Ad hoc item using a Likert-scaled response.
In both sexually active and inactive women, masturbation is not associated with sexual satisfaction (psychological and physiological).No covariates.Ad hoc item to assess the frequency of masturbation."During the past 6 months, how often, on average, have you engaged in the following sexual activities?" The behaviors included masturbation, and the response options for all items were 1 = not at all, 2 = less than once a month, 3 = once or twice a month, 4 = about once a week, 5 = more than once a week, and 6 = daily.
Two ad hoc items to assess the emotional and physical facets of sexual satisfaction."In the past 6 months, how emotionally satisfying was your relationship with your partner?" and "In the past 6 months, how physically pleasurable was your relationship with your partner?"The options were 1 (not at all), 2 (slightly), 3 (moderately), 4 (very), and 5 (extremely).
Men who are less physically satisfied with their partners masturbate more often than men who are more physically satisfied with their partners.This is not observed in women.Covariates in the regression model: age and biopsychosocial variables.All options on the Kinsey scale were considered.
Ad hoc.Masturbation frequency was assessed with an item with 9 options: less than once a year, once a year, once every 6 months, once every 3 months, once or twice a month, once a week, 2 to 3 times a week, once a day, and more than once a day.
The Female Sexual Quotient instrument designed and validated in a previous project [43].It contains 10 questions covering different areas of women's sexual activity.The options for the 10 items are on a Likert-type scale of 5 points.The scores divide sexual performance into five categories: highly dissatisfied (0-20 points), dissatisfied (22-40 points), average (42-60 points), partially satisfied (62-80 points), and highly satisfied (82-100 points).
There is a positive correlation between masturbation frequency and sexual satisfaction.Ad hoc item: "How often do you masturbate?" Responses employed a 9-point rating scale from 1 (more than once a day) to 9 (never).

The French version of the Multidimensional Sexuality
Questionnaire [45] The frequency of solitary sex was negatively correlated with sexual satisfaction.Structural equation modeling: attachment, representation of sexuality, frequency of sexual activities and desire, and sexual satisfaction.Covariates: age, duration of the relationship, and marital satisfaction.
Ad hoc item."All things considered, how satisfied are you with your sexual life?" with response options ranging from 1 = very dissatisfied to 5 = very satisfied.
In single men, there was no relationship between masturbation and sexual satisfaction, while in single women, a positive relationship was observed.In both men and women with a partner, there was no relationship between the frequency of masturbation and sexual satisfaction.Heterosexual.
Ad hoc item.The frequency of masturbation was assessed using a scale that ranged from 0 = never or once a year to 4 = once or more times per day.
Ad hoc item.Sexual satisfaction was rated on a seven-point Likert-type scale (1 = not at all satisfied; 7 = absolutely satisfied).
No relationship is observed between the frequency of masturbation and sexual satisfaction, neither in correlations nor in regression models, while controlling for the frequency of other variables under consideration.Those who answered moderately dissatisfied or very dissatisfied were classified as dissatisfied.
In men, a positive relationship is observed between the frequency of masturbation and being dissatisfied with their overall sex life.In women, no significant relationship is found.Adjusted for age and self-rated health.Ad hoc item.Before and after the quarantine, an ordinal multiple-choice question (<1, 1-2, 3-5, >5/week) graded the masturbatory sexual frequency.
The Female Sexual Quotient (FSQ) [43] and the Male Sexual Quotient (MSQ) [56] were used.Both instruments were developed in Brazilian Portuguese.Questions express the satisfaction level, contemplating the sexual response cycle phases.Responses ranged from 0 = never to 5 = always.
A higher frequency of masturbation is associated with poorer sexual satisfaction in both men and women.Covariates in the regression model: lack of nightlife (clubs, bars, restaurants), lower libido, isolation from partner, working at a central institute, higher sexual frequency, and sexually active.Not specified.
Ad hoc item: "Please rate how often you DO or GET each of the listed sexual activities: sexually touching myself (e.g., masturbation)." Responses ranged from 1 = not at all to 7 = a lot.
Four questions from the Satisfaction with Sex Life Scale-Revised [58] and from [45]: In most ways, my sexual life is close to my ideal.

•
The conditions of my sexual life are excellent.Four questions about sexual functioning and sexual relationships are based on the Derogatis Interview for Sexual Functioning (DISF-SR) [60] and the Changes in Sexual Functioning Questionnaire (CSF) [61].
"During the last six months, how satisfied have you been with. ..:" • Your own capability to give yourself when you have sex.

•
Your own capability to experience sexual lust.

•
The quality of your sex life.

•
The total relationship with current or last sex partner.
Responses to sexual satisfaction items on a 6-point scale ranged from could not have been better to clearly unsatisfactory with an answer option for having not had any sex partner.Not specified.
Ad hoc item to rate their frequency of masturbation using a scale from 1 = never to 8 = multiple times a day.
One item from the Female Sexual Function Inventory (FSFI) [63]: "Over the past 4 weeks, how satisfied have you been with your overall sexual life?" referring to the past four weeks.
Not specified.
Ad hoc item.Days in the past month engaged in masturbation, and days in past month orgasm from activity of masturbation.
Sexual satisfaction was measured in two ways:

•
The full sexual satisfaction scale of the Multidimensional Sexuality Questionnaire (MSQ) [45].

•
A single item from the scale "I am very satisfied with the sexual aspects of my life", similar to the single item from the Life Satisfaction Scale LiSat-11 [39] used in the Swedish study [37].
Both are rated on a five-point scale of agreement to disagreement.
No predictive capacity of masturbation is observed to explain the two measures of sexual satisfaction, both separately and together, in both men and women.Ad hoc item.Participants were asked whether they had sexual activity alone that included masturbation within the last 24 h or since they last completed a diary.This item was coded as 0 = no masturbation today and 1 = masturbation today.

Vaillancourt
Global Measure of Sexual Satisfaction [67] was used to evaluate participants' general global satisfaction.
There is no observed relationship between masturbation and sexual satisfaction for 'actor' and 'partner' separately.Neither self-masturbation nor partner's masturbation had the capacity to explain sexual satisfaction.The use of pornography (yes/no) is controlled for.
Ad hoc item.The frequency of masturbation was assessed on a 6-point scale: never, less than once a month, once to three times a month, once to twice a week, three to four times a week, and five times a week and more.

Ad hoc item.
A single item assesses the degree to which participants were satisfied with their sexual lives.It was answered on a scale ranging from 0 to 100, with lower scores indicating lower satisfaction.
In both men and women, an actor effect of masturbation frequency was observed to explain sexual satisfaction negatively.

Study Selection
The database search yielded 851 records (see Supplementary Data S1).After eliminating duplicates, 464 records remained according to their title, abstract, and keywords.Of these, 432 records were excluded due to the exclusion criteria.A total of 32 underwent a full-text examination, and, finally, 10 were eliminated because they did not meet the inclusion criteria.To broaden the selection process, although a search was made for the papers cited in the studies to be considered, none of them were included.This left 22 papers that met the inclusion criteria and methodological quality standards and could, therefore, be included in the present systematic review.Figure 1 shows a flow chart of the selection process for these studies.

Study Selection
The database search yielded 851 records (see Supplementary Data S1).After eliminating duplicates, 464 records remained according to their title, abstract, and keywords.Of these, 432 records were excluded due to the exclusion criteria.A total of 32 underwent a full-text examination, and, finally, 10 were eliminated because they did not meet the inclusion criteria.To broaden the selection process, although a search was made for the papers cited in the studies to be considered, none of them were included.This left 22 papers that met the inclusion criteria and methodological quality standards and could, therefore, be included in the present systematic review.Figure 1 shows a flow chart of the selection process for these studies.
Below are the results of the 22 analyzed papers that evaluated the relation between solitary masturbation and sexual satisfaction (see Table 1).

Sociodemographic Characteristics
The studies were conducted in one or more of these countries: the United States (5 publications), Norway (4), Brazil (2), Switzerland (1), Sweden (1), Denmark (1), Belgium Below are the results of the 22 analyzed papers that evaluated the relation between solitary masturbation and sexual satisfaction (see Table 1).

Instruments to Assess Masturbation
Most of the studies used ad hoc procedures to assess masturbation: frequency scales and, to a lesser extent, a dichotomous item or an interview to determine presence/absence.Only three papers employed an item drawn from validated scales or found in previous projects to assess masturbation frequency [12,46,47].The time frame to which masturbation practice referred, in those studies that indicated it, was variable: in the last 24 h [66], in the last month [12,36,37,46,59,65], in the last 6 months [41,49,53], or in the last year [15,42].
The remaining six papers used standardized assessment instruments: the Global Measure of Sexual Satisfaction [54] the Female Sexual Quotient [43], which were both included in two papers, the Male Sexual Quotient [56], and the Multidimensional Sexuality Questionnaire (MSQ) [45].

Relation between Masturbation and Sexual Satisfaction
Five studies (22.7%) examined the relation between masturbation and sexual satisfaction in men and women together.They revealed a negative relation [55,57,62,68] or no relation [57,66] between both variables.
Of the studies with samples exclusively made up of men or that examined men independently of women, 71.4% of them (ten articles) reported a negative relation between masturbation and sexual satisfaction [12,16,37,41,44,47,49,53,59,64].In contrast, three studies (21.4%) found no significant relation between the two variables [46,48,65], and a single study (7.2%) observed a positive association between masturbation and sexual satisfaction [15].

Discussion
Solitary masturbation is a behavior with implications for sexual health, among which sexual satisfaction is included.To integrate the results obtained from the scientific literature about the relation between solitary masturbation and sexual satisfaction, this study presents a systematic review of the articles published up to October 2023.Most of the studies included in the review (63.6%) were conducted in the United States and Europe.This aligns with the increasingly positive view in western countries that solitary masturbation is considered to be a source of pleasure that is independent of sexual relationships [1,3,10,69].The evolution toward a positive view of this behavior in recent years has promoted further research, which is reflected by the publication year of the works included in this systematic review because most had publication dates in the last two decades.Nevertheless, masturbation experiences can be positive or negative, depending on prevailing social attitudes [1].The cultural divide observed in this review could be evidence of the challenges in the area of research into sexuality that some societies face, such as African ones, where difficulties are reported for people to share some aspects related to their sexuality [70].Masturbation is still taboo in some of these societies, which contributes to the limited discussion on the topic and the proliferation of many misconceptions about the effects of masturbation, implying disinformation [71].
Most of the participants in the reviewed studies are heterosexuals, which agrees with what has been generally observed in the sexuality research area [72].This scenario reveals that sexual minorities are less represented.In this regard, the importance of integrating groups affected by social stigma in research is highlighted [73].
Solitary masturbation was assessed mostly with one ad hoc item that identified the presence/absence of masturbation or its frequency.Masturbation frequency has been stressed as a relevant measure for investigating masturbation [26,74].This relevant parameter is related to significant indicators of sexual well-being, highlighting its relevance to sexual functioning.In women, the frequency of masturbation is positively related to orgasm pleasure [75] and to the greater facility of reaching orgasm in older women [74].In men, more frequent masturbation is associated with more difficulty reaching an orgasm [74] and more symptoms of retarded ejaculation [76].Therefore, this parameter has contributed to expanding scientific knowledge about masturbation and delving deeper into the study of this behavior [2].However, we should bear in mind the diversity of time ranges and the responses employed to measure this parameter when comparing and generalizing the results reported in the present systematic review.
Sexual satisfaction was often assessed with ad hoc items about the level of experienced satisfaction.This matter has been criticized by Sánchez-Fuentes et al. [19].Using a single item can present measurement stability problems [77], and it may generate sources of error when simplifying the evaluated construct [78].Four works employed items taken from standardized scales, which does not guarantee suitable psychometric properties for the original instrument.Only 27% of the studies evaluated sexual satisfaction using standardized scales, which ensure that acceptable and reliable measures are obtained [79].Of these scales, the Female Sexual Quotient [43], the Male Sexual Quotient [56], and the Multidimensional Sexuality Questionnaire (MSQ) [45] appeared.We stress the Global Measure of Sexual Satisfaction [54], used in two studies.It is a measure included in the Interpersonal Exchange Model of Sexual Satisfaction Questionnaire (IEMSSQ) [80] that derives from the Interpersonal Exchange Model of Sexual Satisfaction (IEMSS) [23], a theoretical consolidated model of sexual satisfaction [67] that has been validated in Spain [81,82], Canada [23], and the United States [83].Considering the complexity of the conceptualization of sexual satisfaction and the diverse ways of assessing it [84], it is highly relevant to integrate its definition to compare and delve into the study of this sexual functioning dimension [85].
In relation to the obtained findings about the relation between solitary masturbation and sexual satisfaction, the studies that jointly considered men and women pointed out a negative relation between solitary masturbation and sexual satisfaction [55,57,62,68] or no relation [57,66].Despite some studies including gender as a covariable (e.g., [57,62]), the results must be cautiously considered given the known differences between men and women in the various parameters associated with masturbation [26,74,[86][87][88][89][90].
The findings in those studies that examined the relation between solitary masturbation and sexual satisfaction in men and women separately are more interesting.Most of the studies (71.4%) that have dealt with this association in men reported a negative relation between solitary masturbation and satisfaction, as opposed to 21.4% of them that did not find a significant relation and the 7.2% that reported a positive association.Thus, a negative relation was observed mostly for men, which contrasts with the evidence showing that masturbation is a positive indicator of sexual health [1] and practicing masturbation is related to different beneficial health aspects (e.g., [91][92][93]).One of the main hypotheses that could explain this finding in men stems from the compensatory model of masturbation [8,15].This model proposes that people resort to this behavior as a substitute for sexual dissatisfaction.Previous evidence reveals that the compensatory pattern of masturbation might be more characteristic of men than women [9,[12][13][14].To support this hypothesis, more men compared to women have reported having less desire to masturbate [94] and show a more negative attitude toward masturbation at older ages [74].This stresses the importance of considering the negative attitude toward masturbation (see [95]) when studying this behavior to understand its implication in the sexual satisfaction experience.This finding could also be interpreted in line with the hypothesis put forward by Rowland et al. [64].According to their hypothesis, people who masturbate may exhibit a strong auto-erotic orientation, which could make this behavior more gratifying than sexual relationships.This proposal is coherent with evidence showing that men report more solitary sexual desire than women [26,74,86], they report a higher masturbation frequency (e.g., [74,88]), and among the various reasons for practicing this behavior, sexual pleasure stands out [96].So it is proposed that future studies which examine the relation between solitary masturbation and satisfaction should include the reasons why masturbation is practiced as a mediator variable.
The studies performed with women reflect, to a greater extent, the heterogeneity of the obtained results: 40% found no relation between solitary masturbation and sexual satisfaction, 33.3% found a negative association, and 26.7% pointed out a positive relation between both variables.This greater heterogeneity of the results obtained for women might have something to do with their sexuality compared to that of men, which is generally determined by a larger number of variables [26,[97][98][99], as specifically noted for sexual satisfaction [100].One third of the studies performed with women found a negative association between solitary masturbation and sexual satisfaction.This reveals that sexual dissatisfaction could also be a reason for them to practice masturbation [93].Masturbating could be an indicator of feeling comfortable about one's body and sexuality, which could raise awareness about dissatisfaction or reduce the likelihood of someone exaggerating their sexual satisfaction during sexual relationships [40].The percentage of the studies that report a positive association between solitary masturbation and sexual satisfaction was higher in women (26.7%) than in men (7.1%).In recent decades, inhibition about female sexuality may have lowered [11,15], which would reflect the empowerment role of masturbation noted in women [101,102].
The inconsistency encountered in the obtained results could be partly due to the diversity of the employed measures, and very few of the research works assessed sexual satisfaction with instruments based on robust theoretical models that have demonstrated their invariance in the population of interest.As previously mentioned, the cultural diversity in accepting and practicing masturbation could also be a source for the variation in the results [3], as could considering neither a negative attitude toward masturbation nor the reasons for masturbating to be covariables.Not all the studies contemplated interpersonaltype variables, such as satisfaction with one's relationship, which has been associated with both practicing masturbation [94] and sexual satisfaction [100].Other covariables that should be considered are age, given that this behavior evolves with generational advancement [10,11,14,69], having a partner because of its association with masturbation practice [9,10], and sexual satisfaction [59].In the exploration of the distinction between being single or in a relationship, it has been observed that in the two studies focusing exclusively on single individuals, no significant association between masturbation and sexual satisfaction was found [40,57], while in the studies that considered exclusively samples of couples, they found a positive (e.g., [15]), negative (e.g., [57]), or no relation (e.g., [66]).These findings should be approached with caution due to the diversity of terminology employed (i.e., partner, sex partner, couple, in a relationship) and the limited evidence found in single people.The importance of further study of the relation between masturbation and sexual satisfaction in single individuals is highlighted [57].
Finally, it is worth mentioning that the results must be cautiously considered because the experimental design type of the reviewed studies does not allow case-effect relations to be established.To interpret the findings of our systematic review, it is necessary to bear in mind that the reviewed studies were original scientific articles written only in Spanish and English.Thus, this systematic review did not consider other languages, types of investigations (e.g., narrative and qualitative), or other reviews.As mentioned above, the diverse criteria for masturbation frequency (e.g., the past 30 days or 6 months), the different instruments used to assess sexual satisfaction, and the sample used (mostly heterosexuals) could influence the generalizability of the results.

Conclusions
Our systematic review evidences the relation between solitary masturbation and sexual satisfaction.Although its findings in favor of a negative association are present, considering sexual differences is absolutely necessary.Thus, a more consistent pattern of negative relations is found in men, which supports the compensatory role of masturbation.Conversely, the results for women are more heterogeneous, and there are more pieces of evidence for a positive relation than for men.This finding suggests that solitary masturbation for women could be an indicator that is more related to sexual health, which would support the complementary role between both behaviors (solitary masturbation and sexual relationships).It is necessary to continue research to examine in more depth the association between masturbation and sexual satisfaction, considering partnered masturbation.In future studies, given the relevance of masturbation to sexual satisfaction, it could also be interesting to examine how different patterns of sexual activity (including solitary masturbation and sexual relationships) are associated with sexual satisfaction in a romantic relationship.It would also be relevant to use a validated theoretical model of sexual satisfaction that would also include solitary masturbation frequency and other important parameters like age of masturbation onset, reasons for masturbating, and specific measures that characterize the subjective orgasm experience achieved by masturbation or taking a negative attitude toward this behavior.

Figure 1 .
Figure 1.Flow diagram for the systematic review of searches of databases.

Figure 1 .
Figure 1.Flow diagram for the systematic review of searches of databases.

Table 1 .
Summary of study reviews about the relationship between solitary masturbation and sexual satisfaction.